Electrical contacts



1956 1.. T. RICHARDSON ETAL 2,760,256

ELECTRICAL CONTACTS Original Fild Nov. 28, 1949 0. 6 ELECTRICAL CONTACTS Linwood Richardson, Wauwatosa, and Merle R. Swinehart, Milwaukee, Wis.

Continuation of abandoned application Serial No.

129,816, November 28, 1949. This application Februaryll, 1953, Serial No. 336,292 p Claims. (C 29-1825) plication -Ser. No. 129,816 filed November'28, ;1949,

now abandoned.

As is Well known to thoseskilled inthe art, electrical;

contact elements heretofore have been su bjcct tomany limitations. Excessive arcing,-pitting of the contactsurfaces, tarnishing,; transfer ofmetal between contacts, welding and sticking are but a few of the difliculties encountered. One or more of these diflicultiesmay become troublesome accordingly as the: contacts are subjected to various conditions of use. A particular likelihood of difiiculty'has been the fact that contacts which operated satisfactorily at low currents completely broke downer were considerablydamaged when usedto make and break circuits carrying relatively large currents. This difiiculty 'has' been even more pronounced when it was desired that a set of-contacts retain. their usefulness for a large number of operations. Although various attempts have been made to overcome these shortcomings, none of them has been completely successful.

An object ofthisinvention is to provide improved electrical contacts which are capable of making and breaking circuit a large number of times while carrying relatively high currents.

Another and more specific object of this invention is to provide improved electrical contacts which will make and break 2000 amperes of a 28 volt D. C. resistance load at least 12,000 times before failure.

Another object is to provide electrical contacts of novel composition which will make and break 2200 amperes of a 250 volt, 60 cycle, 50% lagging power factor load, at least 100 times.

A further object is to provide electrical contacts of the aforementioned character which have a high resistance to pitting and bonding or welding.

Other objects and advantages of the invention will hereinafter appear.

The single figure of the accompanying drawing is a highly magnified fragmentary sectional view of an electrical contact embodying our invention.

As a result of extensive experiments we have found that the desirable characteristics of a contact formed of a bonded mass of powdered silver and cadmium oxide can be greatly improved by incorporating therein a quantity of cobalt sulphate. Cobalt sulphate when added in varying amounts to a mixture of powdered silver and cadmium oxide, the whole of which is then compressed and sintered, produces contacts which are capable of repeatedly making and breaking circuits carrying relatively high currents and which further are particularly characterized by their resistance to pitting and their ability to maintain a smooth contact surface.

The relative proportions of the powdered silver, cadmium oxide and cobalt sulphate maybe varied within nited States 1 2,760,256 7 Patented Aug. 28,

certain ranges forthe purpose of adapting the contacts to suit certain requirements. For example, a pair ofelectrical contacts, three-fourths of an inch in diameter, formed of a bonded mass of 87.5 percent by weightof powdered silver, 10 percent byweight of cadmium oxide and 2.5 percentby weight of cobalt sulphate, were-found, to be capable of making and breaking a 2000 ampere,

formed of abonded masswof75 percent by weightof.

' powdered silver, 21.25 percent by weight of cadmium;

oxide and 3.75 percent by .weightof cobalt sulphate-were; found to be highly satisfactory. A pair of-these-contacts, three-fourths of an inch in diameter, werefoundt capable of making and breaking 2200 amperes of a 250;

" volt, 60. cycle, 50% lagging power factoralternating current load at least 100 times. After testing, these con tacts showed no signs of failure and were foundto havt retaineda smooth contact surface ,withoutevidence- 0f": pitting or sticking. Another pair ofcontactaof thecomposition last mentioned, one-half of -an inch in diameter, when used to make 300 amperes and break 50 amperes. of a single phase, 230 volt, alternating current resistance load, :Werev found capable of withstandingat-least,

250,000 operations. 1 p it ..'3 As hereinbefore mentioned, the relative-proportions.

of powdcredsilver, cadmium oxide and cobalbsulphatei may. be variedoveraacertain range.- 'Althoughdessv than 1.25 percent by weight of cobalt sulphate willesubstantially improve the desirabler-characteristics of silvercadmium oxide contacts,-its addition. in the amount o f. from 1.25 percent by weight up to Spercent' by weight of "the entire mass ofthe contact'compositionhasbeen, found to be most desirable. The silver contentmayvary. from to 93 per cent byweight, and thecadmium oxide, content may vary from 5.75 to 23.75 per cent byqweighus The drawing illustrates the manner in which the cobalt sulphate is intermixed with the silver and cadmium oxide of our contacts. Numeral 1 designates a highly magnified fragment of one of our improved contacts. A base or matrix material 2 consisting of compressed and sintered powdered silver has intermixed therethrough particles 3 which are composed of a compressed and sintered mixture of cobalt sulphate and cadmium oxide.

The following is a preferred method of making our improved contacts. However, it is to be understood that this method is set forth by way of example only, it being assumed that other methods of producing contacts having a similar structure and composition will be readily suggested to those skilled in the art.

An intimate mixture of the desired or required proportions of cobalt sulphate and cadmium oxide (each ingredient being in the form of a powder of such fineness that the mixture will pass through a 325 mesh screen) is densified by applying a molding pressure of the order of 100,000 pounds per square inch. The slugs produced in this manner are then subjected to a temperature of 1600 degrees F. for a period of one hour, after which they are ground in such a manner, or to such an extent, that all of the particles thereof will pass through a mesh screen and approximately one-half of the total quantity of said particles will be retained on a 300 mesh screen.

The particles produced in the above-described manner are then intimately mixed with a given quantity of precipitated silver powder. This mixture is subjected to pressure of approximately 100,000 pounds per square inch to produce the completed electrical contacts.

We claim:

1. An electrical contact in the form of a bonded mass of powders composed of a mixture of from seventy-five to ninety-three percent by weight of silver powder, from five and three-fourths to twenty-three and three-fourthspercent by weight of cadmium oxide, and from approximately one and one-fourth percent up to five percent by weight of cobalt sulphate.

2QAn' electrical contact in the form of a bonded mass of powders composed of'a mixture of fromseventy-five to eighty-seven and one-half percent by weight of silver powder, from ten to twenty-three and three-fourths percent by weight of cadmium oxide, and from approximate 1y one and one-fourth percent up to five percent by weight of cobalt sulphate.

3. An electrical contact in the form of a bonded mass of powders composed of a mixture of from eighty-seven and one-half to ninety-three percent by weight of silver powder, from five and three-fourths to ten percent by weight of cadmium oxide, and from one and one-fourth percent up to two and one-half percent by weight of cobalt sulphate.

'4. electricalcontact in the form of a bonded mass 6. An electrical contact for making and breaking electric current, formed of from seventy-five to ninetythree percent by Weight of silver powder, five and three fourths to twentydhree and three-fourths percent by weight of cadmium oxide, and from three and threefourths up to five percent by weight of cobalt sulphate.

7. An electrical contact formaking and breaking electric current, formed of at least seventy-five parts by weight of silver powder, at least five and three-fourths parts by weight of cadmium oxide,and an amount up to five parts of weight of cobalt sulphate.

8. An electrical contact for making and breaking electric current, formed of at least seventy-one andonefourth percent by weight; of silver powder, at least five and three-fourths percent by weight of cadmium oxide, and an amount from one and one=fourth percent up to five percent by weight of cobalt sulphate, said cadmium oxide and cobalt sulphate being in mixture form and said 7 mixture beingdistributed in the form of discrete particles throughout the mass of silver. 9. An electrical contact in the form ofa bonded mass of powders composed of a mixture of from seventy-five to ninety-three percent by weight of silver powder,.

fromfive and three-fourths to twenty-three and threefourths percent by weight of cadmium oxide, and from one and one-fourth percent to five percent by weight of cobalt sulphate; 1 t f p 10. An electrical contact in the form of a bonded it mass of powde rs' composed of from seventy-five to of powders composed of a mixture of from eighty-seven and one-half to ninety-three percent by Weight of silver powder, fromfive and three-fourths to twenty-one and one-fourth percent by weight of cadmium oxide, and from one and one-fourthpercent up to five percent by weight of cobalt sulphate.

5; An electrical contact in the form of a bonded mass ofpowders composed of a mixture of from eighty-seven and one-half toninety-three percent by weight of silver powder, from five and three-fourths to ten percent by weight of cadmium oxide, and from one and one-fourth percent up tothree and three-fourths percent by weight of cobalt sulphate.

ninety-three percent by weight of silver powder, from five andthree-fourths to twenty-three and three-fourths percent by weight ofcadmium oxide,and from one and one-fourth 'to five percent by Weightof cobalt suphate,

said cadmium oxide and cobalt sulphate being in mix ture form and said mixture being distributed in the form of. discrete particles throughoutthe mass of silver.

Y References Cited in the file of this patent UNITED STATES PATENTS 2,151.90": Emmert Mar. 28, 1939 2,418,811 Adams et a1. Apr. 15, 1947 2,425,052 Swinehart Aug. 5, 1947 

1. AN ELECTRICAL CONTACT IN THE FORM OF A BONDED MASS OF POWDERS COMPOSED OF A MIXTURE OF FROM SEVENTY-FIVE TO NINETY-THREE PERCENT BY WEIGHT OF SILVER POWDER, FROM FIVE AND THREE-FOURTHS TO TWENTY-THREE AND THREE-FOURTHS PERCENT BY WEIGHT OF CADIUM OXIDE, AND FROM APPROXIMATELY ONE AND ONE-FOURTH PERCENT UP TO FIVE PERCENT BY WEIGHT OF COBALT SULPHATE. 